1. Field of the Invention
This invention relates generally to wheelchairs and, more particularly, to wheelchairs that are adapted to traverse stepped obstacles.
2. Description of the Related Art
Persons who are confined to wheelchairs can often be confronted with stepped obstacles, such as curbs at street intersections and steps at building entrances. Conventional wheelchairs include a seat supported by two parallel, tubular side frames each having one large rear wheel with a slightly smaller concentric hand wheel for propelling leverage and one small swiveling front wheel for steering. It can be extremely difficult for a wheelchair-bound person to traverse up and over stepped obstacles, and ultimately assistance or an alternate route must often be sought. Many attempts have been made to provide wheelchairs with the ability to negotiate stepped obstacles, but most have drawbacks that have prevented widespread acceptance.
Some step-climbing wheelchairs that can successfully negotiate stepped obstacles bear little resemblance to the conventional wheelchair and comprise expensive, complicated climbing devices. For example, such climbing devices might incorporate deployable ramps that are carried with the climbing device, or might include movable support columns that allow the device to step up and down. Such climbing devices normally are quite heavy, often weighing several hundred pounds. Because of their great weight, they are too heavy for the occupant to roll forward manually, and require propelling assistance from a drive motor. Requirement for a drive motor adds further to the expense of the device. Exemplary stair-climbing devices are described in U.S. Pat. No. 4,222,449 to Feliz and in U.S. Pat. No. 4,618,155 to Jayne.
Some step-climbing wheelchairs are essentially conventional wheelchairs modified with a step-climbing structure at more modest expense than the more complicated climbing devices described above. Such structures can be difficult to adapt to a conventional wheelchair or can be difficult to operate by a wheelchair occupant who has limited motor coordination. For example, some devices comprise ski-like slides that are added to the wheelchair frame or comprise gripping elements that are added to the large wheels. Operation of so-modified wheelchairs could require successive manual deployment and retraction of the climbing elements or could require adjusting the operation of hydraulic valves for raising and lowering the slides, tasks that are not easily performed by someone with limited motor coordination. Exemplary step-climbing wheelchairs are described in U.S. Pat. No. 3,336,128 to Grier and U.S. Pat. No. 3,985,389 to Bonfield.
From the foregoing discussion, it should be apparent that there is a need for an apparatus that allows a wheelchair to traverse stepped obstacles, that can be attached to a conventional wheelchair without extensive modifications, and that is relatively lightweight and easy to operate. The present invention satisfies this need.